The present invention relates to a method for polymerizing pyrrolidone with an anionic catalyst and an accelerator.
Polymerizing pyrrolidone, optionally mixed with another copolymerizable lactam, such as .delta.-valerolactam or .epsilon.-caprolactam, by means of an anionic catalyst and one or more accelerators is already known. The anionic catalyst is, in most cases, an alkali pyrrolidonate. This compound can be made by heating an alkali hydroxide or alkoxide with an excec of pyrrolidone, so that the corresponding pyrrolidonate is formed. The water and/or alcohol formed during the reaction is distilled off as soon as possible at reduced pressure and at a temperature of between 50.degree.-150.degree. C.
A problem in this known method is that the catalyst quality varies, particularly if in the preparation of the catalyst small quantities of oxygen are present, and that .gamma.-amino-butyric acid is formed, an undesirable by-product.
It is thus an object of the invention to make a catalyst of constant quantity, so that reproduceable polymerization will be possible.